Winter

i was just wondering, to do a compression comparison...

if i were to use a 50 shot, in terms of PSI boost, how much is that adding? i know it's about a 50 horse power boost, but psi wise, how much would that be?

the reason i ask is so that i can see what compression ratio that is being added.

seems ZPI had been doing some testing with thier kit and posted some results a year or so ago and mentioned they were puting about 12psi to the stock compression of 10.5:1 which would result in about a 19.1:1 compression at full 12psi. this is where they started having problems with the axels and whatnot. so i figure the 25.0:1 range is probably going to be the danger zone and thus why i'd like to know what a 50 shot would add...

my guess, going by what seems to be what ZPI did when they marketed 180whp on thier kit at 7.5psi before ever testing on the dyno, and then when they tested the dyno, it came to about 178-182whp. seems based on the engine and the way it's built, every 1psi = about 12hp added. so this would mean a 50 shot would be about... 3.8-4.2psi added... right?

that being said, those running with say 9.5:1 compression with say... 17psi boost *based on Garrett's GT2554R turbo used in ZPI, Turbo Toyota and Greddy's kits.* whould be about 20.4-5:1 resulting compression and about 255hp... then lets say you did a 50 shot while being at full 17psi would be another added 3.8-4.2psi boost and going to a compression of about 23.0:1 resulting in about 305 horses. 100 shot being about 8psi added boost resulting in a compression ratio of about 26.0:1 and about 355-360hp.

here where my math comes from... based on compression ratio effect charts with specific amounts of boost added equaling whatever horse power outcome over the stock number *i used 87 wheel horse power for the xB, about 5hp more then most stock xB's i think but close enough.*

compression ratio raise for ever 2psi boost added = +1.2-1.3.0:1
every 1psi added = about 12hp
if ever 1psi added = about 12hp then 50 shot would = about 3.8-4.2psi depending on outside atmosphere and spray temp..

i figure it's safe to say 25.0:1 compression should be a good area to mark as the danger zone for right now for the more hardcore tuners, 20.0:1 for the basic tuners. unless you have some serious custom work done, that 25.0:1 area shouldn't be touched i think being that if you are using 9.5:1 pistons and using 17psi boost, that would be the same thing as the stock 10.5:1 on 14psi boost.

:D

EasysBox

12hp per psi, thats quite a generalization, there are a lot of other factors that come into play. in the same motor in the same trim, you can run both at say 8 psi, using two different kits, and you will get two totally different hp numbers...

Winter

i understand that, thats why i based this off of kits that were very simular to each other, as in the lines of the GT2554R turbo. the same turbo that ZPI, TT and Greddy use fo thier kits on this specific engine. but the numbers are not backed by actual dyno tests, they are estimates that should be within a 5-10% accuracy range of what you would really get.

only real diffrence between the kits is placement except for the Greddy kit which doesn't use an intercooler capable enough for more then 12psi boost, replace the intercooler, wastegate and BOV and it would basicly be about the same as the other two kits.

but like i said, this is an about statement that is infact actualy acurate enough to get a general idea to work with but nothing to be used to completely base everything on. this is mainly about the compression, 19.0-20.0:1 being the point of serious problems like broke axels, shattered rods and such. the 25.0:1 zone being for those who have heavy mods done with other piece not available for aftermarket thats been custom made for it. i say about 25.0:1 area because thats having the need for say 115octane fuel just to use. i based that off of the highest fuel rating i know of in my area which is Chevron's racing fuel at like 6 bucks a gallon.

but as for the 12hp per psi, check on the post done some time ago about ZPI doing thier R&D tests and whatnot. get thier figures and use a compression ratio chart - http://www.motion-dynamics.net/boost_vs_comp_ratio.jpg like so and do the math, it's all there, not exactly accurate, but it's a good idea of what to expect atleast within a 10% accuracy range.